Air conditioning device

ABSTRACT

In an air conditioning device ( 1 ) that includes: a PTC heater ( 55 ) in which, in a stable region (S 1 ), when the temperature of the PTC heater ( 55 ) is increased, a resistance is decreased or is substantially constant whereas, in a rise region (S 2 ), the resistance is rapidly increased when the temperature exceeds a rise temperature (T 1 ); and an air blower ( 25 ) that generates an air current which exchanges heat with the PTC heater ( 55 ), and that performs a heating operation by discharging air heated by the PTC heater ( 55 ) into the room, when the temperature within the room is within a low temperature range including a region whose temperature is lower than a set temperature, the duty ratio is set at 100%, and the PTC heater ( 55 ) is driven in the rise region (S 2 ), when the temperature within the room is within a high temperature range whose temperatures are higher than the set temperature, the PTC heater ( 55 ) is stopped, and when the temperature within the room is within an intermediate temperature range between the low temperature range and the high temperature range, the duty ratio is set at a predetermined duty ratio, and the PTC heater ( 55 ) is driven in the stable region (S 1 ).

This nonprovisional application claims priority under 35 U.S.C. §119 (a) on Patent Application No. 2010-132608 filed in Japan on Jun. 10, 2010, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an air conditioning device including a PTC heater.

2. Description of the Related Art

A conventional air conditioning device is disclosed in JP-A-H08-152179. This air conditioning device is integrally formed such that an indoor portion within a room is arranged in its front portion and an outdoor portion outside the room is arranged in its rear portion. In the outdoor portion, a compressor that operates a refrigeration cycle and an outdoor heat exchanger that is connected to the compressor are arranged. An inlet port and an outlet port are open in the indoor portion; an air blower, an indoor heat exchanger and a PTC (positive temperature coefficient) heater are arranged within the indoor portion. The indoor heat exchanger is connected to the compressor through a refrigerant pipe. The air blower sucks in air through the inlet port, and discharges, through the outlet port, the air that has exchanged heat with the indoor heat exchanger and the PTC heater.

When a cooling operation is started, the compressor is driven and thus the refrigeration cycle is operated, the indoor heat exchanger functions as an evaporator on the low temperature side of the refrigeration cycle, and the outdoor heat exchanger functions as a condenser on the high temperature side of the refrigeration cycle. Air within the room flows, by driving of the air blower, into the indoor portion through the inlet port; the air whose temperature is decreased by exchanging heat with the indoor heat exchanger is discharged through the outlet port into the room. In this way, the room is cooled.

When a heating operation is started, the compressor is driven and thus the refrigeration cycle is operated, the indoor heat exchanger functions as a condenser on the high temperature side of the refrigeration cycle, and the outdoor heat exchanger functions as an evaporator on the low temperature side of the refrigeration cycle. The air within the room flows, by driving of the air blower, into the indoor portion through the inlet port, and the air is increased in temperature by exchanging heat with the indoor heat exchanger. The air that has flowed into the indoor portion by driving of the PTC heater is further increased in temperature. The heated air is discharged through the outlet port into the room, and thus the room is heated.

The PTC heater is formed by sandwiching a heating element having a PTC characteristic between electrodes; voltage is applied across the electrodes to drive the PTC heater. In a stable region, when the temperature of the heating element is increased, the resistance of the heating element is decreased or is substantially constant whereas, in a rise region, the resistance is rapidly increased when the temperature exceeds a rise temperature.

When the PTC heater is driven in the rise region and thus its temperature is increased, the resistance of the heating element is rapidly increased, and the current and the amount of heat generated are decreased; when its temperature is decreased, the resistance of the heating element is rapidly decreased, and the current and the amount of heat generated are increased. In this way, the amount of heat generated by the PTC heater becomes constant, and thus it is possible not only to easily produce warm air having a predetermined temperature but also to prevent the PTC heater from being overheated.

However, in the conventional air conditioning device described above, when the temperature within the room exceeds the set temperature, the heating ability of the PTC heater is reduced whereas when the temperature within the room drops below the set temperature, the heating ability of the PTC heater is enhanced. Here, when the heating ability of the PTC heater is changed by voltage, a temperature drop resulting from a decrease in voltage causes the resistance of the heating element to be rapidly reduced, and an overcurrent flows through the PTC heater, with the result that the power supply capacity is disadvantageously exceeded.

On the other hand, when the heating ability of the PTC heater is changed by the volume of air blown by the air blower, if the temperature within the room is increased, the number of revolutions of the air blower is decreased whereas if the temperature within the room is decreased, the number of revolutions of the air blower is increased. Here, since the PTC heater continues to produce a predetermined amount of heat, the temperature near the air conditioning device is increased, with the result that the temperature within the room disadvantageously becomes uneven.

Hence, when the compressor is stopped in the heating operation, the average heating ability of the PTC heater is kept high and the heating is performed only by the PTC heater, an overcurrent is produced or the temperature within the room becomes uneven. It is therefore common to decrease the average heating ability of the PTC heater, drive the compressor and use the PTC heater in an auxiliary manner. Thus, it is likely that the ability of the PTC heater can not be sufficiently utilized and that the heating ability is reduced such as when the outside temperature is low.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an air conditioning device that can make a temperature within a room uniform and prevent an overcurrent from flowing through a PTC heater.

To achieve the above object, according to the present invention, there is provided an air conditioning device including: a PTC heater in which, in a stable region, when a temperature of the PTC heater is increased, a resistance of the PTC heater is decreased or is substantially constant whereas, in a rise region, the resistance is rapidly increased when the temperature exceeds a rise temperature; a heater control portion that controls a duty ratio of the PTC heater; a temperature detection portion that detects a temperature within a room; and an air blower that generates an air current which exchanges heat with the PTC heater. In the air conditioning device, a heating operation is performed by discharging air heated by the PTC heater into the room, when the temperature within the room is within a low temperature range including a region whose temperature is lower than a set temperature, the duty ratio is set at 100%, and the PTC heater is driven in the rise region, when the temperature within the room is within a high temperature range whose temperatures are higher than the set temperature, the PTC heater is stopped, and when the temperature within the room is within an intermediate temperature range between the low temperature range and the high temperature range, the duty ratio is set at a predetermined duty ratio, and the PTC heater is driven in the stable region.

In this configuration, when the heating operation is started, the PTC heater and the air blower are driven. The air current generated by the air blower exchanges heat with the PTC heater, and the air heated by the PTC heater is discharged into the room. The duty ratio of the PTC heater is controlled by the heater control portion; when the temperature within the room detected by the temperature detection portion is within the low temperature range including the region whose temperature is lower than the set temperature, the PTC heater is driven at a duty ratio of 100%. Here, the temperature of the PTC heater is kept at the temperature in the rise region where the resistance is rapidly changed as the temperature changes. Thus, it is possible to stabilize the amount of heat generated by the PTC heater and to prevent the PTC heater from being overheated.

When the temperature within the room is increased to reach the intermediate temperature range, the PTC heater is driven at a predetermined duty ratio. Here, the temperature of the PTC heater is kept at the temperature in the stable region where, when the temperature is increased, the resistance is decreased or is substantially constant, and thus the amount of heat generated by the PTC heater is decreased. Since the duty ratio is reduced until the temperature within the room reaches the temperature in the stable region, the resistance of the PTC heater is decreased but the current is reduced, and thus an overcurrent is prevented from being produced. When the temperature within the room is further increased to reach the high temperature range, the PTC heater is stopped, and the temperature of the PTC heater is reduced.

Preferably, in the air conditioning device of the present invention configured as described above, the intermediate temperature range is further divided into a plurality of auxiliary temperature ranges, and, when the temperature within the room is within a high temperature-side auxiliary temperature range, the duty ratio of the PTC heater is set lower than a duty ratio at the time of a low temperature-side auxiliary temperature range. In this configuration, the temperature within the room reaches the low temperature-side auxiliary temperature range of the intermediate temperature range, the PTC heater is driven at a predetermined duty ratio. When the temperature within the room is increased to reach the high temperature-side auxiliary temperature range of the intermediate temperature range, the PTC heater is driven at a duty ratio that is obtained by decreasing the duty ratio by a predetermined amount from the low temperature-side auxiliary temperature range.

Preferably, in the air conditioning device of the present invention configured as described above, when the temperature within the room is within the high temperature-side auxiliary temperature range, the number of revolutions of the air blower is changed such that the number of revolutions of the air blower is lower than the number of revolutions of the air blower at the time of the low temperature-side auxiliary temperature range. In this configuration, when the temperature of the PTC heater is decreased in the high temperature-side auxiliary temperature range because the duty ratio is reduced, the number of revolutions of the air blower is decreased, and cold air is prevented from being discharged.

Preferably, in the air conditioning device of the present invention configured as described above, when the temperature within the room is within the high temperature range, the number of revolutions of the air blower is changed such that the number of revolutions of the air blower is lower than the number of revolutions of the air blower at the time of the low temperature range. In this configuration, when the temperature is decreased in the high temperature range due to the stop of the PTC heater, the number of revolutions of the air blower is decreased, and cold air is prevented from being discharged. The air blower may be stopped in the high temperature range.

Preferably, in the air conditioning device of the present invention configured as described above, a current detection portion that detects a current which flows through the PTC heater is further provided, and processing in which, in an early stage after the temperature within the room enters the low temperature range, the duty ratio is set higher than a duty ratio at the time of the intermediate temperature range, and in which, when the current detected by the current detection portion is lower than a predetermined value, the duty ratio is increased by a predetermined amount is repeated until the duty ratio reaches 100%.

In this configuration, when the temperature within the room reaches the low temperature range, the heater control portion applies, for example, a voltage at a duty ratio of 50% to the PTC heater. The current detection portion detects the current through the PTC heater at predetermined intervals, and, when the current through the PTC heater is lower than a predetermined value, the duty ratio is increased by, for example, 10%. This processing is repeated and thus the duty ratio is gradually increased, and, when the duty ratio reaches 100%, the PTC heater is driven.

Preferably, in the air conditioning device of the present invention configured as described above, in the early stage after the temperature within the room enters the low temperature range, the air blower is driven at the first number of revolutions, until the duty ratio of the PTC heater reaches 100%, the number of revolutions of the air blower is gradually decreased from the first number of revolution, and, when the duty ratio of the PTC heater reaches 100%, the air blower is driven at the second number of revolutions that is larger than the first number of revolution.

In this configuration, when the temperature within the room reaches the low temperature range, the air blower is rotated at the first number of revolutions, and the number of revolutions is gradually reduced, with the result that the air blower is rotated at a low speed. Then, when the duty ratio of the PTC heater reaches 100%, the air blower is rotated at the second number of revolutions, that is, at a high speed.

Preferably, in the air conditioning device of the present invention configured as described above, when the current detected by the current detection portion is higher than a predetermined value, the duty ratio of the PTC heater is decreased by a predetermined amount. In this configuration, when the current detected by the current detection portion is higher than the predetermined value, the duty ratio of the PTC heater is decreased by, for example, 10%. Thus, it is possible to prevent an overcurrent from flowing through the PTC heater.

Preferably, in the air conditioning device of the present invention configured as described above, a compressor that operates a refrigeration cycle and a heat exchanger that exchanges heat with the air current generated by the air blower in a high temperature part of the refrigeration cycle are provided, and the air conditioning device can switch between a heating operation performed by driving of the compressor and a heating operation performed by driving of the PTC heater, and, when the heating operation by driving of the compressor is performed and the temperature within the room is lower than a predetermined temperature, the heating operation is switched to the heating operation by driving of the PTC heater.

In this configuration, the compressor and the air blower are driven to perform the heating operation, and the compressor is driven to operate the refrigeration cycle. The air current generated by the air blower exchanges heat with the heat exchanger, and the air heated by the heat exchanger is discharged into the room. In a predetermined period after the heating operation by driving of the compressor is performed, the temperature detection portion detects the temperature within the room. When the temperature within the room is lower than the predetermined temperature, the compressor is stopped and the PTC heater is driven, and the air that has exchanged heat with the PTC heater is discharged into the room.

Preferably, in the air conditioning device of the present invention configured as described above, when the heating operation is started, the heating operation by driving of the PTC heater is performed, and, when the temperature within the room becomes higher than a predetermined temperature, the heating operation is switched to the heating operation by driving of the compressor. In this configuration, when the air conditioning device starts to perform the heating operation, the air that has exchanged heat with the PTC heater by driving of the PTC heater is discharged into the room. When the temperature within the room becomes higher than the predetermined temperature, the PTC heater is stopped and the compressor is driven, and the air that has exchanged heat with the heat exchanger is discharged into the room. Then, when the temperature within the room becomes lower than the predetermined temperature, the compressor is stopped and the PTC heater is driven.

In the present invention, the duty ratio is set at 100% in the low temperature range and the PTC heater is driven in the rise region; the PTC heater is stopped in the high temperature range; and the duty ratio is set at a predetermined duty ratio in the intermediate temperature range and the PTC heater is driven in the stable region. Thus it is possible not only to stabilize the amount of heat generated by the PTC heater in the low temperature range to prevent the PTC heater from being overheated but also to prevent an overcurrent from being produced in the intermediate temperature range. Since the temperature of the PTC heater is not kept at a high temperature, it is possible to prevent the temperature near the air conditioning device from being increased and to make the temperature within the room uniform.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing an air conditioning device of a first embodiment;

FIG. 2 is a side cross-sectional view showing the air conditioning device of the first embodiment;

FIG. 3 is a block diagram showing the configuration of the air conditioning device of the first embodiment;

FIG. 4 is a diagram showing the temperature characteristic of the resistance of a PTC heater in the air conditioning device of the first embodiment;

FIG. 5 is a flowchart showing the operation of a heating operation of the air conditioning device of the first embodiment;

FIG. 6 is a flowchart showing the operation of a heating operation of an air conditioning device of a second embodiment;

FIG. 7 is a flowchart showing the operation of a heating operation of the air conditioning device of a third embodiment;

FIG. 8 is a flowchart showing the operation of duty variation processing on the air conditioning device of the third embodiment;

FIG. 9 is a time chart on the duty variation processing on the air conditioning device of the third embodiment; and

FIG. 10 is a flowchart showing the operation of a heating operation of an air conditioning device of a fourth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIGS. 1 and 2 show a perspective view and a side cross-sectional view, respectively, of an air conditioning device of a first embodiment. FIG. 1 shows a state where an outer cover 30 (see FIG. 2) is removed. The air conditioning device 1 is integrally formed so as to have an indoor portion 2 that is arranged within a room and an outdoor portion 4 that is adjacent to the indoor portion 2 and arranged outside the room.

In the front surface of the indoor portion 2, an inlet port 21 is provided; in the front surface of the outdoor portion 4, an outdoor heat exchanger 42 is provided. In the following description, the side of the inlet port 21 is referred to as a front side, and the side of the outdoor heat exchanger 42 is referred to as a rear side (back surface side). The right side and the left side as seem from a position opposite the front surface of the inlet port 21 are referred to as the right side and the left side of the air conditioning device 1.

The indoor portion 2 and the outdoor portion 4 are placed on a bottom plate 3, and they are separated, one in front of the other, by a separation wall 5. In the indoor portion 2, an enclosure 20 is formed that covers the outside of the indoor portion 2 with the bottom plate 3, the separation wall 5 and the outer cover 30. Likewise, in the outdoor portion 4, an enclosure 40 is formed that covers the outside of the outdoor portion 4 with the bottom plate 3, the separation wall 5 and an outer cover (not shown).

In the outdoor portion 4, a compressor 41 that operates a refrigeration cycle is arranged in an end portion in the right side. In the back surface of the outdoor portion 4, the outdoor heat exchanger 42, which is connected to the compressor 41 through a refrigerant pipe 47, is arranged. An outdoor fan 43 that is formed with a propeller fan is so arranged in the center portion in a right and left direction as to face the outdoor heat exchanger 42, and cools the outdoor heat exchanger 42. The outdoor fan 43 and the outdoor heat exchanger 42 are arranged within a housing 44, and the housing 44 forms a duct that guides an air current from the outdoor fan 43 to the outdoor heat exchanger 42. The housing 44 is supported by the separation wall 5 through brackets 45.

The inlet port 21 is open in the front surface of the outer cover 30 covering the indoor portion 2; an outlet port 22 is open above the inlet port 21. Within the indoor portion 2, a blower duct 24 through which the inlet port 21 is coupled to the outlet port 22 forms a blower passage 23. The blower duct 24 has, in its upper portion, a duct member 29 that can be freely detached when the outer cover 30 is removed; the duct member 29 forms a lower wall near the outlet port 22 of the blower passage 23.

Within the blower passage 23, an indoor fan 25 (air blower) formed with a cross flow fan is provided. In the vicinity of the outlet port 22 within the blower passage 23, a louver 26 is provided that can change the direction of an air current. An indoor heat exchanger 27 that is connected to the compressor 41 through the refrigerant pipe 47 is arranged between the indoor fan 25 and the inlet port 21.

A heating portion 28 that has a plurality of PTC heaters 55 (see FIG. 3) is arranged between the indoor fan 25 and the indoor heat exchanger 27. The indoor fan 25 forms, in the blower passage 23, an air current that is passed through the inlet port 21 and that exchanges heat with the PTC heaters 55 and the indoor heat exchanger 27. The duct member 29 covers the top of the indoor heat exchanger 27 and the heating portion 28. When the duct member 29 is removed, the heating portion 28 can be freely detached.

FIG. 3 is a block diagram showing the configuration of the air conditioning device 1. The air conditioning device 1 includes a control portion 50 that controls portions of the air conditioning device 1. The compressor 41, the indoor fan 25, the outdoor fan 43, an operation portion 51, a storage portion 52, a current detection portion 53, a heater control portion 54 and a temperature detection portion 56 are connected to the control portion 50. The PTC heaters 55 of the heating portion 28 are connected to the heater control portion 54.

The operation portion 51 is formed with an operation button and a remote controller provided on the surface of the enclosure 20; through the operation portion 51, an instruction to operate the air conditioning device 1 is provided and a setting is input. The storage portion 52 is formed with a ROM and a RAM; the storage portion 52 stores a program for operating the air conditioning device 1 and setting conditions and the like, and performs temporary storage during the computation of the control portion 50. Although the storage portion 52 is connected to the outside of the control portion 50, the storage portion 52 may be provided within the control portion 50.

The current detection portion 53 detects a current flowing through the PTC heaters 55. The heater control portion 54 controls the driving of the PTC heaters 55. The temperature detection portion 56 detects the temperature within the room. The heater control portion 54 is formed with a triac circuit or a relay circuit, and controls the duty ratio of the PTC heaters 55. The heater control portion 54 is preferably formed with the tiac circuit because this makes it possible to reduce a sound resulting from switching as compared with the relay circuit.

The PTC heater 55 is formed by sandwiching a heating element having a PTC characteristic between electrodes; a drive voltage is applied, by the heater control portion 54, across the electrodes, and thus heat is produced. FIG. 4 shows the temperature characteristic of the resistance of the PTC heater 55. The vertical axis represents the resistance; the horizontal axis represents the temperature. In a stable region S1, when the temperature of the PTC heater 55 is increased, the resistance is decreased or is substantially constant whereas, in a rise region S2, the resistance is rapidly increased when the temperature exceeds a rise temperature T1.

In the air conditioning device 1 configured as described above, when a cooling operation is started, the compressor 41 is driven and thus the refrigeration cycle is operated. Thus, the indoor heat exchanger 27 functions as an evaporator on the low temperature side of the refrigeration cycle, and the outdoor heat exchanger 42 functions as a condenser on the high temperature side of the refrigeration cycle. The outdoor heat exchanger 42 is cooled by the outdoor fan 43 to discharge heat. The air within the room flows, by driving of the indoor fan 25, through the inlet port 21 into the blower passage 23; the air whose temperature is decreased by exchanging heat with the indoor heat exchanger 27 is discharged through the outlet port 22 into the room. In this way, the room is cooled.

The air conditioning device 1 can switch between a heating operation performed by driving of the compressor 41 and a heating operation performed by driving of the PTC heaters 55, and thereby perform the heating operation. When the compressor 41 is driven, the refrigeration cycle is operated. Thus, the indoor heat exchanger 27 functions as a condenser on the high temperature side of the refrigeration cycle, and the outdoor heat exchanger 42 functions as an evaporator on the low temperature side of the refrigeration cycle. The outdoor heat exchanger 42 exchanges heat with outside air by the outdoor fan 43, and absorbs heat. The air within the room flows, by driving of the indoor fan 25, through the inlet port 21 into the blower passage 23, and the air is increased in temperature by exchanging heat with the indoor heat exchanger 27. The air heated by the indoor heat exchanger 27 is discharged through the outlet port 22 into the room.

When the PTC heaters 55 are driven, the air within the blower passage 23 is increased in temperature by the PTC heaters 55. The air heated by the PTC heaters 55 is discharged through the outlet port 22 into the room.

Although the heating operation performed by driving of the compressor 41 can reduce power consumption as compared with the heating operation performed by driving of the PTC heaters 55, since the outdoor heat exchanger 42 does not sufficiently absorb heat when the temperature of the outside air is low, the heating ability is reduced. Hence, when the temperature of the outside air is high, the heating operation by driving of the compressor 41 is performed whereas when the temperature of the outside air is low, the heating operation by driving of the PTC heaters 55 is performed.

FIG. 5 is a flowchart showing the operation of the heating operation performed by driving of the PTC heaters 55. A different type of control is performed on the PTC heaters 55 and the indoor fan 25 in each of a low temperature range, an intermediate temperature range and a high temperature range into which the temperature within the room is divided. The low temperature range is formed with a predetermined temperature range including a region whose temperatures are lower than the set temperature for the temperature within the room. The high temperature range is formed with a predetermined temperature range whose temperatures are higher than the set temperature for the temperature within the room. The intermediate temperature range is formed with a temperature range between the low temperature range and the high temperature range.

For example, a boundary temperature between the low temperature range and the intermediate temperature range is set at the set temperature for the temperature within the room, and a boundary temperature between the intermediate temperature range and the high temperature range is set at a temperature that is 2° C. higher than the set temperature for the temperature within the room. Consequently, the low temperature range is a temperature range that is equal to or less than the set temperature, the intermediate temperature range is a temperature range that ranges from the set temperature to the set temperature +2° C. and the high temperature range is a temperature range that is equal to or more than the set temperature +2° C. The boundary temperature between the low temperature range and the intermediate temperature range may be set higher than the set temperature for the temperature within the room. The boundary temperature when the temperature is decreased may be reduced by a predetermined temperature (for example, 1° C.) from the boundary temperature when the temperature is increased. Thus, it is possible to stabilize the operation of the PTC heaters 55 around the boundary temperature.

In step #21, the temperature within the room is detected by the temperature detection portion 56. In step #22, whether or not the temperature within the room is within the low temperature range is determined. If the temperature within the room is within the low temperature range, in step #23, the duty ratio of the PTC heaters 55 is set at 100%, and the PTC heaters 55 are driven. In step #36, the indoor fan 25 is driven to produce a strong air current (for example, 1140 RPM), and the process returns to step #21.

Here, the temperature of the PTC heaters 55 is kept at the temperature in the rise region S2 (see FIG. 4). Thus, when the temperature of the PTC heaters 55 are increased, the resistance of the heating elements is rapidly increased, and the current and the amount of heat generated are decreased whereas, when the temperature is decreased, the resistance of the heating elements is rapidly decreased, and the current and the amount of heat generated are increased. Hence, the amount of heat generated by the PTC heaters 55 becomes constant, and thus it is possible not only to easily produce warm air having a predetermined temperature but also to prevent the PTC heaters 55 from being overheated.

If, in step #22, the temperature within the room is determined not to be within the low temperature range, the process moves to step #31. In step #31, whether or not the temperature within the room is within the intermediate temperature range is determined. If the temperature within the room is within the intermediate temperature range, in step #35, the duty ratio of the PTC heaters 55 is set at 40%, and the PTC heaters 55 are driven. In step #36, the indoor fan 25 is driven to produce a strong air current, and the process returns to step #21.

Here, the temperature of the PTC heaters 55 is kept at the temperature in the stable region S1 (see FIG. 4), and the amount of heat generated by the PTC heaters 55 is reduced. Since the duty ratio is reduced such that the temperature in the stable region S1 is reached, the resistance of the PTC heaters 55 is decreased but the current is reduced. Thus, an overcurrent is prevented from flowing through the PTC heaters 55.

If, in step #31, the temperature within the room is determined not to be within the intermediate temperature range, the temperature within the room is within the high temperature range, and hence the process moves to step #41. In step #41, the PTC heaters 55 are stopped (duty ratio of 0%). In step #42, the indoor fan 25 is driven to produce a soft air current (for example, 300 RPM), and the process returns to step #21. Thus, the discharge of cold air resulting from the temperature of the PTC heaters 55 being reduced is prevented.

In step #42, the indoor fan 25 may be stopped. Here, it is preferable to stop the indoor fan 25 a predetermined period of time (for example, 30 seconds) after the PTC heaters 55 are stopped because heat is not left within the indoor portion 2.

In the present embodiment, the duty ratio is set at 100% in the low temperature range and the PTC heaters 55 are driven in the rise region S2; the PTC heaters 55 are stopped in the high temperature range; and the duty ratio is set at a predetermined duty ratio in the intermediate temperature range and the PTC heaters 55 are driven in the stable region S1. Thus it is possible not only to stabilize the amount of heat generated by the PTC heaters 55 in the low temperature range to prevent the PTC heaters 55 from being overheated but also to prevent an overcurrent from being produced in the intermediate temperature range. Since the temperature of the PTC heaters 55 is not kept at a high temperature, it is possible to prevent the temperature near the indoor portion 2 of the air conditioning device 1 from being increased and to make the temperature within the room uniform.

Hence, the compressor 41 is stopped, the PTC heaters 55 are only driven and thus the heating operation can be performed. Therefore, the ability of the PTC heaters 55 is fully used, and thus it is possible to prevent the heating ability from being reduced such as when the temperature of outside air is low.

Since the number of revolutions of the indoor fan 25 (air blower) is reduced in the high temperature range as compared with the low temperature range, it is possible to prevent cold air from being discharged due to the stop of the PTC heaters 55 and to prevent an uncomfortable feeling from being given to the user.

FIG. 6 is a flowchart showing the operation of a heating operation performed by driving of the PTC heaters 55 of an air conditioning device 1 according to a second embodiment. The configuration of the air conditioning device 1 of the present embodiment is the same as described in the first embodiment shown in FIGS. 1 to 5 described previously except that a control method used when the temperature within the room is within the intermediate temperature range is different. In the present embodiment, the intermediate temperature range obtained by diving the temperature within the room is further divided into two auxiliary temperature ranges, and different types of control are performed on the PTC heaters 55 and the indoor fan 25. In the figure, since steps #21 to #23 and step #41 are the same as shown in FIG. 5 described previously, their description will not be repeated.

If, in step #31, the temperature within the room is determined to be within the intermediate temperature range, the process moves to step #32. In step #32, whether or not the temperature within the room is within a low temperature-side auxiliary temperature range is determined. If the temperature within the room is within the low temperature-side auxiliary temperature range, in step #35, the duty ratio of the PTC heaters 55 is set at 40%, and the PTC heaters 55 are driven. In step #36, the indoor fan 25 is driven to produce a strong air current, and the process returns to step #21.

If, in step #32, the temperature within the room is determined not to be within the low temperature-side auxiliary temperature range, the temperature within the room is within a high temperature-side auxiliary temperature range, and the process moves to step #37. In step #37, the duty ratio of the PTC heaters 55 is set at 30%, and the PTC heaters 55 are driven. In step #42, the indoor fan 25 is driven to produce a soft air current, and the process returns to step #21.

In the present embodiment, the intermediate temperature range is further divided into a plurality of auxiliary temperature ranges, the duty ratio in the high temperature-side auxiliary temperature range is set at 30% that is lower than that in the low temperature-side auxiliary temperature range and the PTC heaters 55 are driven. Thus, it is possible to more finely adjust the amount of heat supplied to the room according to the temperature within the room and to more stably maintain the temperature within the room.

Since the number of revolutions of the indoor fan 25 (air blower) is reduced in the high temperature-side auxiliary temperature range as compared with the low temperature-side auxiliary temperature range, it is possible to prevent cold air from being discharged due to a decrease in the temperature of the PTC heaters 55 and to prevent an uncomfortable feeling from being given to the user. When the duty ratio is set at 30% but the temperature within the room is increased, in step #41, the PTC heaters 55 are stopped. Here, the indoor fan 25 may be stopped.

Although, in the present embodiment, the intermediate temperature range is divided into the two auxiliary temperature ranges, the intermediate temperature range may be divided into three or more auxiliary temperature ranges, and the PTC heaters 55 may be driven at different duty ratios.

FIG. 7 is a flowchart showing the operation of a heating operation performed by driving of the PTC heaters 55 of an air conditioning device 1 according to a third embodiment. The air conditioning device 1 of the present embodiment is operated in the same manner as in the second embodiment shown in FIG. 6 described previously except that a control method used when the temperature within the room is within the low temperature range is different. In the figure, since steps #21 and #22 and steps #31 to #42 are the same as shown in FIG. 6 described previously, their description will not be repeated.

If, in step #22, the temperature within the room is determined to be within the low temperature range, the process moves to step #25 where duty variation processing shown in FIG. 8 is performed. FIG. 9 is a time chart when the duty variation processing is performed. FIG. 9( a) shows a duty ratio (unit: %) of a drive voltage of the PTC heaters 55. FIG. 9( b) shows a current (represented by “I” in the figure) detected by the current detection portion 53 and the temperature (represented by “T” in the figure) of the PTC heaters 55.

In step #51, in the early stage of the duty variation processing, the indoor fan 25 is driven at the first number of revolutions (for example, 600 RPM) to produce a soft air current. In step #52, the PTC heaters 55 start being driven at a duty ratio of 50% that is higher than that in the intermediate temperature range (time t0). Thus, the temperature of the PTC heaters 55 is increased, and the current flowing through the PTC heaters 55 is increased until the temperature of the heating elements reaches the rise temperature T1 (see FIG. 4).

The heater control portion 54 acquires a result of detection by the current detection portion 53 at intervals of a predetermined period (one second in the present embodiment); in step #53, the heater control portion 54 is placed on standby until the predetermined period elapses. After the predetermined period elapses, in step #54, the current detected by the current detection portion 53 is acquired. In step #55, whether or not the current acquired from the current detection portion 53 is higher than a predetermined current value I1 is determined. The current value I1 is set based on a power supply capacity; when the current exceeds the current value I1, an overcurrent state where a large amount of current flows through the PTC heaters 55 and the power supply capacity may be exceeded is produced.

If the predetermined period that is the interval for the acquisition of the result of the detection by the current detection portion 53 in step #53 is too short, a burden is placed on the control. On the other hand, if the predetermined period is too long, during standby, the current flowing through the PTC heaters 55 may be excessively increased or may be excessively decreased. Hence, in the present embodiment, the predetermined period is set at one second. It is preferable to determine an appropriate period by experiment according to the configuration of the air conditioning device 1.

If the current acquired from the current detection portion 53 is higher than the current value I1, in step #56, the duty ratio of the PTC heaters 55 is reduced only by 10% (which indicates 10% with respect to 100%). Thus, it is possible to come out of the overcurrent state, and the process returns to step #53.

If the current acquired from the current detection portion 53 is not higher than the current value I1, in step #57, whether or not the current is lower than a predetermined current value I2 is determined. The current value I2 is set lower than the current value I1. If the current acquired from the current detection portion 53 is lower than the predetermined current value I2, the process moves to step #58.

When the temperature of the PTC heaters 55 is increased and the temperature of the heating elements exceeds the rise temperature T1, the resistance of the heating elements is increased, and the current through the PTC heaters 55 reaches a local maximum value P (see FIG. 9( b)). Hence, if the current acquired from the current detection portion 53 becomes lower than the current value acquired in the preceding round, the current is determined to reach the local maximum value P, and the process moves to step #59. If the current acquired from the current detection portion 53 is not lower than the current value acquired in the preceding round, the process returns to step #53.

In step #59, the duty ratio of the PTC heaters 55 is increased only by 10% (which indicates 10% with respect to 100%). Since the duty ratio is increased, the current through the PTC heaters 55 is increased again. The duty ratio of the PTC heaters 55 may be increased by a value other than 10%.

In step #60, whether or not the duty ratio of the PTC heaters 55 reaches 100% is determined. If the duty ratio of the PTC heaters 55 does not reach 100%, the process returns to step #53, and steps #53 to #60 are repeated. Then, as described above, when the temperature of the PTC heaters 55 is increased, the resistance is increased, and the current through the PTC heaters 55 reaches the local maximum value P. In this way, the duty ratio of the PTC heaters 55 is increased by 10% each time the process comes to step #59, and the current is gradually increased.

If the duty ratio of the PTC heaters 55 reaches 100%, the process returns to the flowchart of FIG. 7. In step #36 of FIG. 7, the indoor fan 25 is driven at a second number of revolutions (for example, 1140 RPM) larger than the first number of revolutions so as to produce a strong air current. Here, the amount of cooling by the PTC heaters 55 is increased, and the temperature T of the PTC heaters 55 is slightly reduced.

If, in step #57, the current acquired from the current detection portion 53 is determined not to be lower than the current value I2, the process returns to step #53. In other words, the duty ratio of the PTC heaters 55 is maintained regardless of the occurrence of the local maximum value P. Hence, the duty ratio is neither increased nor decreased between the current value I1 and the current value I2, and thus it is possible to prevent the overcurrent state from being produced.

In the present embodiment, in the early stage after the movement to the low temperature range, driving is performed at a duty ratio higher than the duty ratio in the intermediate temperature range; and, when the current through the PTC heaters 55 is lower than the predetermined current value I2, the duty ratio is increased only by the predetermined amount, and this is repeated until the duty ratio reaches 100%. Hence, even when the temperature of the PTC heaters 55 is low, such as when the PTC heaters 55 are started, the current is gradually increased, and thus it is possible to prevent an overcurrent from being produced and to prevent the current from exceeding the power supply capacity.

Since, when the current through the PTC heaters 55 reaches the local maximum value P, the duty ratio is increased, the timing of increasing the duty ratio is prevented from being early, and thus it is possible to reliably prevent an overcurrent from being produced such as when the PTC heaters 55 are started.

In the early stage of the duty variation processing, the indoor fan 25 is driven at the first number of revolutions (for example, 600 RPM), and, when the duty ratio of the PTC heaters 55 reaches 100%, the indoor fan 25 is driven at the second number of revolutions (for example, 1140 RPM), which is larger than the first number of revolutions. The volume of air blown by the indoor fan 25 is reduced in the early stage, and thus the exchange of heat between the PTC heaters 55 and the air is facilitated. It is therefore possible to increase the rate at which the temperature of the PTC heaters 55 is increased.

Since, if the current acquired from the current detection portion 53 is higher than the current value I1, in step #56, the duty ratio is reduced, it is possible to come out of the overcurrent state of the PTC heaters 55 and to more reliably prevent the current from exceeding the power supply capacity.

FIG. 10 is a flowchart showing the operation of a heating operation performed by an air conditioning device 1 according to a fourth embodiment. The air conditioning device 1 of the present embodiment can switch between the heating operation performed by driving of the compressor 41 and the heating operation performed by driving of the PTC heaters 55. The heating operation by driving of the PTC heaters 55 is performed in the same manner as described in the third embodiment of FIGS. 7 to 9 described previously; since the steps #21 to #42 are the same as shown in FIG. 7, and their description will not be repeated.

When the heating operation is started, in step #11, the indoor fan 25 is driven to produce a strong air current. In step #12, the temperature within the room is detected by the temperature detection portion 56. In step #13, whether or not the temperature within the room is within the high temperature range is determined. If the temperature within the room is not within the high temperature range, in step #14, the duty ratio of the PTC heaters 55 is set at 100%, and the PTC heaters 55 are driven. In this way, the heating operation by driving of the PTC heaters 55 is performed. Then, the process returns to step #11, and steps #11 to #14 are repeated.

If the temperature within the room enters the high temperature range, the process moves to step #15 where the PTC heaters 55 are stopped. In step #16, the compressor 41 is driven. Thus, the heating operation by driving of the compressor 41 is performed. In step #17, the temperature within the room is detected by the temperature detection portion 56. In step #18, whether or not the temperature within the room is within the low temperature range is determined.

If the temperature within the room is not within the low temperature range, steps #17 and #18 are repeated. The ability of the compressor 41 is changed according to the temperature within the room, and the compressor 41 is driven such that the temperature within the room is kept near the set temperature. Here, since the temperature within the room changes near the set temperature, in order to prevent the temperature within the room from often entering the low temperature range, the boundary temperature between the low temperature range and the intermediate temperature range is set such that the boundary temperature is reduced by a predetermined temperature (for example, 1° C.) from the set temperature for the temperature within the room.

If the temperature within the room enters the low temperature range, in step #19, the compressor 41 is stopped. Then, in steps #21 to #42, the operation is switched to the heating operation performed by driving of the PTC heaters 55. If the temperature within the room enters the high temperature range while the PTC heaters 55 are being driven, the process moves to step #15 by the determination made in step #31. Thus, the PTC heaters 55 are stopped, and the operation is switched to the heating operation performed by driving of the compressor 41.

In the present embodiment, since, when the temperature within the room is lower than the predetermined temperature, the heating operation performed by driving of the compressor 41 is switched to the heating operation performed by driving of the PTC heaters 55, it is possible to reduce the power consumption by performing the heating operation by driving of the compressor 41 near the set temperature. When the temperature within the room cannot be kept near the set temperature by driving of the compressor 41, the PTC heaters 55 are driven, and thus it is possible to keep the temperature at the set temperature.

When the heating operation is started, the heating operation by driving of the PTC heaters 55 is performed, and, when the temperature within the room becomes higher than the predetermined temperature, the operation is switched to the heating operation performed by driving of the compressor 41. Therefore, the PTC heaters 55 are driven at a low temperature when the air conditioning device 1 is started, and thus it is possible to rapidly increase the temperature within the room.

The present invention can be applied to air conditioning devices having PTC heaters.

LIST OF REFERENCE NUMERALS

-   -   1 AIR CONDITIONING DEVICE     -   2 INDOOR PORTION     -   3 BOTTOM PLATE     -   4 OUTDOOR PORTION     -   5 SEPARATION WALL     -   20 ENCLOSURE     -   21 INLET PORT     -   22 OUTLET PORT     -   23 BLOWER PASSAGE     -   24 BLOWER DUCT     -   25 INDOOR FAN     -   26 LOUVER     -   27 INDOOR HEAT EXCHANGER     -   28 HEATING PORTION     -   30 OUTER COVER     -   41 COMPRESSOR     -   42 OUTDOOR HEAT EXCHANGER     -   43 OUTDOOR FAN     -   47 REFRIGERANT PIPE     -   50 CONTROL PORTION     -   51 OPERATION PORTION     -   52 STORAGE PORTION     -   53 CURRENT DETECTION PORTION     -   54 HEATER CONTROL PORTION     -   55 PTC HEATER     -   56 TEMPERATURE DETECTION PORTION 

1. An air conditioning device comprising: a PTC heater in which, in a stable region, when a temperature of the PTC heater is increased, a resistance of the PTC heater is decreased or is substantially constant whereas, in a rise region, the resistance is rapidly increased when the temperature exceeds a rise temperature; a heater control portion that controls a duty ratio of the PTC heater; a temperature detection portion that detects a temperature within a room; and an air blower that generates an air current which exchanges heat with the PTC heater, wherein a heating operation is performed by discharging air heated by the PTC heater into the room, when the temperature within the room is within a low temperature range including a region whose temperature is lower than a set temperature, the duty ratio is set at 100%, and the PTC heater is driven in the rise region, when the temperature within the room is within a high temperature range whose temperatures are higher than the set temperature, the PTC heater is stopped, and when the temperature within the room is within an intermediate temperature range between the low temperature range and the high temperature range, the duty ratio is set at a predetermined duty ratio, and the PTC heater is driven in the stable region.
 2. The air conditioning device of claim 1, wherein the intermediate temperature range is further divided into a plurality of auxiliary temperature ranges, and, when the temperature within the room is within a high temperature-side auxiliary temperature range, the duty ratio of the PTC heater is set lower than a duty ratio at the time of a low temperature-side auxiliary temperature range.
 3. The air conditioning device of claim 2, wherein, when the temperature within the room is within the high temperature-side auxiliary temperature range, a number of revolutions of the air blower is changed such that the number of revolutions of the air blower is lower than a number of revolutions of the air blower at the time of the low temperature-side auxiliary temperature range.
 4. The air conditioning device of claim 1, wherein, when the temperature within the room is within the high temperature range, a number of revolutions of the air blower is changed such that the number of revolutions of the air blower is lower than a number of revolutions of the air blower at the time of the low temperature range.
 5. The air conditioning device of claim 1, further comprising: a current detection portion that detects a current which flows through the PTC heater, wherein processing in which, in an early stage after the temperature within the room enters the low temperature range, the duty ratio is set higher than a duty ratio at the time of the intermediate temperature range, and in which, when the current detected by the current detection portion is lower than a predetermined value, the duty ratio is increased by a predetermined amount is repeated until the duty ratio reaches 100%.
 6. The air conditioning device of claim 5, wherein, in the early stage after the temperature within the room enters the low temperature range, the air blower is driven at a first number of revolutions, until the duty ratio of the PTC heater reaches 100%, the number of revolutions of the air blower is gradually decreased from the first number of revolution, and when the duty ratio of the PTC heater reaches 100%, the air blower is driven at a second number of revolutions that is larger than the first number of revolution.
 7. The air conditioning device of claim 5, wherein, when the current detected by the current detection portion is higher than a predetermined value, the duty ratio of the PTC heater is decreased by a predetermined amount.
 8. The air conditioning device of claim 1, further comprising: a compressor that operates a refrigeration cycle; and a heat exchanger that exchanges heat with the air current generated by the air blower in a high temperature part of the refrigeration cycle, wherein the air conditioning device can switch between a heating operation performed by driving of the compressor and a heating operation performed by driving of the PTC heater, and when the heating operation by driving of the compressor is performed and the temperature within the room is lower than a predetermined temperature, the heating operation is switched to the heating operation by driving of the PTC heater.
 9. The air conditioning device of claim 8, wherein, when the heating operation is started, the heating operation by driving of the PTC heater is performed, and when the temperature within the room becomes higher than a predetermined temperature, the heating operation is switched to the heating operation by driving of the compressor. 